598 research outputs found
Dynamical Casimir-Polder energy between an excited and a ground-state atom
We consider the Casimir-Polder interaction between two atoms, one in the
ground state and the other in its excited state. The interaction is
time-dependent for this system, because of the dynamical self-dressing and the
spontaneous decay of the excited atom. We calculate the dynamical
Casimir-Polder potential between the two atoms using an effective Hamiltonian
approach. The results obtained and their physical meaning are discussed and
compared with previous results based on a time-independent approach which uses
a non-normalizable dressed state for the excited atom.Comment: 11 page
Non locality and causal evolution in QFT
Non locality appearing in QFT during the free evolution of localized field
states and in the Feynman propagator function is analyzed. It is shown to be
connected to the initial non local properties present at the level of quantum
states and then it does not imply a violation of Einstein's causality. Then it
is investigated a simple QFT system with interaction, consisting of a classical
source coupled linearly to a quantum scalar field, that is exactly solved. The
expression for the time evolution of the state describing the system is given.
The expectation value of any arbitrary ``good'' local observable, expressed as
a function of the field operator and its space and time derivatives, is
obtained explicitly at all order in the field-matter coupling constant. These
expectation values have a source dependent part that is shown to be always
causally retarded, while the non local contributions are source independent and
related to the non local properties of zero point vacuum fluctuations.Comment: Submitted to Journal of Physics B: 16 pages: 1 figur
Causality and Localization Operators
The evolution of the expectation values of one and two points scalar field
operators and of positive localization operators, generated by an istantaneous
point source is non local. Non locality is attributed either to zero point
vacuum fluctuations, or to non local operations or to the microcausality
principle being no satisfied.Comment: 10 pages; submitted to Physics Letters
The limits of the rotating wave approximation in the electromagnetic field propagation in a cavity
We consider three two-level atoms inside a one-dimensional cavity,
interacting with the electromagnetic field in the rotating wave approximation
(RWA), commonly used in the atom-radiation interaction. One of the three atoms
is initially excited, and the other two are in their ground state. We
numerically calculate the propagation of the field spontaneously emitted by the
excited atom and scattered by the second atom, as well as the excitation
probability of the second and third atom. The results obtained are analyzed
from the point of view of relativistic causality in the atom-field interaction.
We show that, when the RWA is used, relativistic causality is obtained only if
the integrations over the field frequencies are extended to ; on the
contrary, noncausal tails remain even if the number of field modes is
increased. This clearly shows the limit of the RWA in dealing with subtle
problems such as relativistic causality in the atom-field interaction.Comment: 13 pages, 6 figure
Loss of coherence and dressing in QED
The dynamics of a free charged particle, initially described by a coherent wave packet, interacting with an environment, i.e. the electromagnetic field characterized by a temperature , is studied. Using the dipole approximation the exact expressions for the evolution of the reduced density matrix both in momentum and configuration space and the vacuum and the thermal contribution to decoherence, are obtained. The time behaviour of the coherence lengths in the two representations are given. Through the analysis of the dynamic of the field structure associated to the particle the vacuum contribution is shown to be linked to the birth of correlations between the single momentum components of the particle wave packet and the virtual photons of the dressing cloud
Loss of coherence and dressing in QED
The dynamics of a free charged particle, initially described by a coherent wave packet, interacting with an environment, i.e., the electromagnetic field characterized by a temperature T, is studied. Using the dipole approximation, the exact expressions for the evolution of the reduced density matrix both in momentum and configuration space and the vacuum and the thermal contribution to decoherence are obtained. The time behavior of the coherence lengths in the two representations are given. Through the analysis of the dynamic of the field structure associated with the particle the vacuum contribution is shown to be linked to the birth of correlations between the single momentum components of the particle wave packet and the virtual photons of the dressing clou
Casimir-Polder potentials as entanglement probe
We have considered the interaction of a pair of spatially separated two-level
atoms with the electromagnetic field in its vacuum state and we have analyzed
the amount of entanglement induced between the two atoms by the non local field
fluctuations. This has allowed us to characterize the quantum nature of the non
local correlations of the electromagnetic field vacuum state as well as to link
the induced quantum entanglement with Casimir-Polder potentials.Comment: Published on Europhysics Letters 78 (2007) 3000
Distillation by repeated measurements: continuous spectrum case
Repeated measurements on a part of a bipartite system strongly affect the
other part not measured, whose dynamics is regulated by an effective contracted
evolution operator. When the spectrum of this operator is discrete, the latter
system is driven into a pure state irrespective of the initial state, provided
the spectrum satisfies certain conditions. We here show that even in the case
of continuous spectrum an effective distillation can occur under rather general
conditions. We confirm it by applying our formalism to a simple model.Comment: 4 pages, 2 figure
Time-dependent Casimir-Polder forces and partially dressed states
A time-dependent Casimir-Polder force is shown to arise during the time
evolution of a partially dressed two-level atom. The partially dressed atom is
obtained by a rapid change of an atomic parameter such as its transition
frequency, due to the action of some external agent. The electromagnetic field
fluctuations around the atom, averaged over the solid angle for simplicity, are
calculated as a function of time, and it is shown that the interaction energy
with a second atom yields a dynamical Casimir-Polder potential between the two
atoms
"THE ROLE OF GREEN EXPERIENTIAL QUALITY, SATISFACTION, AND AUTHENTICITY ON TOURISTS PRO-ENVIRONMENTAL INTENTION"
This research investigates the impact of green experiential quality, experiential satisfaction, and perceived authenticity on tourists’ pro-environmental behavior. Based on an extension of the service quality framework, experiential quality related to green practices represents an extension that goes beyond the tourists’ evaluation of the functional attributes provided by the hospitality sector and the hotel suppliers. In fact, it reflects the tourists’ affective response to their desired socio-psychological benefits linked to the ability of the hospitality offering to consider the specific consumers’ sustainable needs. The preliminary findings are based on 300 green hotel customers and data are analyzed through a moderated-mediated analysis conducted via PROCESS macro for SPSS. Our results confirm the role of green experiential quality in driving the tourist towards pro-environmental behavior during the tourism experience. It does so via the mediation role played by the consequent experiential satisfaction deriving from the hotel green practices quality. Surprisingly, our findings found no support for the moderating role of authenticity in fostering the relationship between green quality and perceived satisfaction. Our study suggests valuable insights for both managers and scholars related to the antecedents of pro-environmental behavior deriving from hotel green practices
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